Servicing apparatus for gas cooled thermal reactors



Feb. 2, 1965 D. J. INGRAM 3,

SERVICING APPARATUS FOR GAS COOL-ED THERMAL REACTORS Original Filed Sept. 25, 1957 8 Sheets-Sheet 1 m P v l I l \9 5 oo oo o o l 11 88 88888 8 88- H 6 QC 000 o 00} L l. 88% 8 800 88:

I D 7 88 80888 8 88 I 00000 0 888, 00000 000 8 0000 coo Feb. 2, 1965 D. J. INGRAM 3,158,444

SERVICING APPARATUS FOR GAS COOLED THERMAL. REACTORS Original Filed Sept. 25, 1957 8 Sheets-Sheet 3 i 39 E! :71 w 42 28 n m INVENTOK 2W 0/0W M D. J. INGRAM 8 Sheets-Sheet 4 'NVENTQ Diva) (/m-hv 2144;, 424 an n ro Ys Feb. 2, 1965 SERVICING APPARATUS FOR GAS COOLED THERMAL REACTORS Original Filed Sept. 25, 1957 D. J. INGRAM Feb. 2, 1965 SERVICING APPARATUS FOR GAS COOLED THERMAL REACTORS 8 Sheets-Sheet 5 Original Filed Sept. 25, 1957 NVENTUK D m ID mv G (H 4 3 D. J. INGRAM Feb. 2, 1965 SERVICING APPARATUS FOR GAS COOLED THERMAL REACTORS 8 Sheets-Sheet 6 Original Filed Sept. 25, 1957 D. J. INGRAM Feb. 2, 1965 SERVICING APPARATUS FOR GAS COOLED THERMAL REACTORS Original Filed Sept. 25, 1957 8 Sheets-Sheet 7 7 s 4 w 8 y F C m M. w m 7 6 WM 8 8 J r 4 w B 2) 5 3 4 44 .w 2 0.. 5 7 IIPIIWHII. v v. ,IulIMi! N h m A 6 7 4 6 6 Feb. 2, 1965 D. J. INGRAM 3,168,444

SERVICING APPARATUS FOR GAS COOLED THERMAL REACTORS Original Filed Sept. 25, 1957 8 Sheets-Sheet 8 I H vb?! =amaniial EFis .ll IIHM U- hil -val...

l I, .-ai ihuiii i n ii. u. J

INVENYEK Dav/9 mv /-6Rn-r 2344:. diam United States Patent Ofifice asserts Patented Feb. 2, 1965 3,168,444 SERVICING APFARATUS FOR GAS COGLED THERMAL REACTORS David John Ingram, Barnehnrst, Kent, England, assignor to The General Electric Company Limited, London, England (Zontinuation of application Ser. No. 686,073, Sept. 25, 1957. This application Nov. 27, 1961, Ser. No. 155,106 Claims priority, application Great Britain, Sept. 27, 1956, 29,608/56 8 Claims. ((11. 176-32) This application is a continuation of my copending application Serial No. 686,073, filed September 25, 1957, now abandoned.

This invention relates to nuclear reactors having within an enclosing shell a core of moderating material provided with channels arranged to contain a plurality of fuel elements, cooling medium being arranged to fiow through the said channels and abstract heat from the fuel elements during operation of the nuclear reactor. Each fuel element will contain fissile material such as U or Pu or U and will generally be clad with a material such as magnesium alloy which is corrosion-resistant and absorbs comparatively few neutrons. The cooling medium, which may be gaseous, may pass to heat exchangers after cooling the fuel elements, the heat given up by the medium in the heat exchangers being available for the generation of steam for use in a turbo-alternator plant.

In a nuclear reactor of this kind, it is generally necessary to provide a large number of channels containing fuel elements and a further substantial number of channels, usually parallel to the main fuel element channels, for rods of boron loaded steel or similar material of high neutron capture cross-section, for control of the operation of the reactor. Since both fuel elements and control rods must at some time be replaced or renewed, it is necessary to provide some convenient means for achieving these purposes and it has been proposed in the specifications accompanying application Serial Nos. 596,114, dated July 5, 1956, and 661,882, dated May 27, 1957, both now abandoned, to provide at least one travelling auxiliary vessel capable of being sealed onto the said enclosing shell at any one of a number of points and capable of having its interior conditions matched to conditions prevailing in the said enclosing shell, for the purpose of carrying out some operation or operations on the reactor. In the said specification, a construction of reactor is disclosed in which an auxiliary vessel below the reactor enclosing shell serves for both fuel element charging and discharging purposes and a further auxiliary vessel above the enclosing shell serves for changing the control rods and for control rod mechanisms. The specification of co-pending application Serial No. 686,072, dated September 25, 1957, now abandoned, discloses a preferred construction of power means which may be stowed within the lower auxiliary vessel and is adapted for fuel element charging and discharging purposes; an object of the present invention is the provision of an auxiliary vessel eminently suitable for servicing control rods and performing other allied servicing operations.

According to the present invention, in or for a nuclear reactor of the kind having within an enclosing shell a core of moderating material provided with channels arranged to contain a plurality of fuel elements, cooling medium being arranged to flow through the said channels and abstract heat from the fuel elements during operation of the nuclear reactor, there is provided a travelling auxiliary vessel capable of attachment to the said enclosing shell at any one of a number of points so that the interior conditions of the said vessel and the said shell may be matched and communication therebetween made through a passage, a plurality of separate or distinct servicing Hal mechanisms for carrying out a number of difierent service operations upon the reactor being housed within the said vessel offset from the axis of the said passage when inoperative and arranged to be brought individually onto or near the said axis when it is required to carry out a servicing operation through the said passage.

The servicing mechanisms may lie round an inner substantially cylindrical wall of the vessel when inoperative and may be arranged to be brought on to or near the axis of the cylindrical wall when it is required to carry out a servicing operation. For this purpose a parallel link motion may be employed for bringing the servicing mechanisms into operation.

Although such a travelling auxiliary vessel may be used in conjunction with a nuclear reactor having a core provided with, for example, horizontal channels it is principally intended to form part of a nuclear reactor which has a core with substantially vertical fuel element channels and further substantially vertical channels for control rods of neutron absorbing material. In this case, the vessel will be disposed above the reactor core as envisaged in the aforementioned specifications of applications Serial Nos. 596,114, dated July 5, 1956, and 661,882, dated May 27, 1957. The servicing mechanisms may then include means for raising control rods and associated equipment out of the enclosing shell and for efifecting their replacement means for recovering control rods detached from their cables, means for lowering thermocouple fuel elements into the fuel element channels etc. Means may be included for lowering and operating a pneumatic ram or a camera in the fuel element channels of the reactor core, and if the power means described in the specification of application Serial No. 686,072, dated September 25, 1957, is to be used in conjunction with a lower auxiliary vessel, the servicing mechanisms may include means for lowering a grab right through the reactor core to the power means partially or wholly stowed within the auxiliary vessel, so as to retrieve fuel elements.

The travelling auxiliary vessel, which may conveniently be termed a reactor servicing machine, is preferably positioned outside the main biological shield of the reactor and all servicing mechanisms within the vessel may be sufficiently shielded to allow personnel to approach the vessel while it is in operation, although it will also be generally convenient to arrange that all the servicing mechanisms may be operated from a position remote from the vessel itself.

One construction of reactor servicing machine in accordance with the present invention will now be described by way of example with reference to the 13 figures of the accompanying drawings, in which identical parts have been given the same reference numerals. The drawings are confined to illustrating details of the servicing machine and show only as much of the core of a nuclear reactor in which the servicing machine is considered to be embodied as is necessary to illustrate the method of operation of the servicing mechanisms within the machine. In the drawings:

FIGURES 1 and 2 show the general layout of the machine above the reaetor core, FIGURE 1 being a top plan view of the machine and FIGURE 2 being a section on the line lIII of FIGURE 1.

FIGURE 3 shows a diagrammatic top plan View of the servicing machine with the cap removed.

FIGURE 4 shows in diagrammatic form a sectional plan view of the interior of the servicing machine taken generally a little above the main lifting drums of the servicing mechanisms.

FIGURES 5 and 6 show somewhat diagrammatically how a complete control rod mechanism is raised within the reactor core and stored within the servicing machine.

FIGURE 7 illustrates the normal position of the control J) rod mechanism within the reactor and two stages in retrieving and removing from the enclosing shell a control rod detached from its cable.

FIGURES 8 and 9 show, in a similar manner to FIG- URES and 6, how a distance tube or a detached control rod is removed and stored within the servicing machine.

FIGURES and 11 show two separate telescopic tube mechanisms within the servicing machine.

FIGURE 12 shows the operation of one telescopic tube mechanism employed for general purposes.

FIGURE 13 shows stages in the insertion of a thermocouple fuel element into the reactor core by means of the other telescopic tube mechanism.

Referring now to FIGURES 1 and 2 of the drawings, the reactor servicing machine comprises a travelling auxiliary vessel 1 capable of attachment to a main shell of the reactor core, which is disposed beneath a concrete biological shield 2, through a plurality of standpipes 3. The vessel 1 is mounted on a travelling carriage 4 provided with three motor driven levelling jacks 5 (FIGURE 1), the carriage 4 running on rails 6 transversely of a travelling gantry 7 itself moving along longitudinal rails 8 so that a communicating passage or outlet tube 9 (FIG- URE 2) of the vessel 1 may be disposed directly above any one of the standpipes 3. The tops of these standpipes 3 are widened out and contain control rod mechanisms as described hereinafter; in connecting the passage 9 to the widened tops of these standpipes 3, use is made of a spacer sleeve 11, including a bellows coupling 10, which fits over the top of the standpipe and is sealed by a gastight union to a flange 12 on the standpipe. Mechanisms within the vessel 1 are shielded so that personnel may approach the vessel, for which purpose a platform is provided. Above the platform are a number of drive units 13 for the servicing mechanisms within. These drive units are electrically operated from a control desk 14 situated at a position remote from the vessel 1 itself. A further travelling gantry 15 moving on longitudinal rails 16 forms part of a crane having three transversely travelling hoists 17. These hoists, which are of varying size, perform a variety of tasks such as the manipulation of the spacer sleeve 11, removal of the top cap 18 of the vessel 1 when required, and the handling of cofiins for irradiated articles such as control rods removed from the reactor core. On first removal from the core, such rods are stored in socalled mortuary holes 19 until the radiation they emit has appreciably died down, after which they are placed in cofiins (not shown), and discharged through a well 20 into a cooling pond at the side of the reactor. Two walkways 21 are also provided, and these walkways are capable of transverse movement along rails 22.

A plan view of the interior of the travelling vessel 1 is shown in FIGURE 3. It will be seen that there are six servicing mechanisms which lie round the inner cylindrical wall of the vessel 1 when they are in the inoperative condition in which they are shown in FIGURES 3 and 4. Drive units 13 are arranged in two pairs on either side of each servicing mechanism, the individual units of each pair being arranged vertically beneath each other. Each drive unit comprises an electric motor and gear box indicated generally at 23 together with a gas-tight coupling 24-. It will be convenient to refer in turn to each servicing mechanism and describe the function it performs before considering the mechanisms in detail. Proceeding round the vessel in a clockwise direction, therefore, the function of each mechanism is as follows:

I. General purpose telescopic tubes for ramming, etc.

II. Means for the withdrawal or replacement of control rods and associated equipment.

III. Means for recovering detached control rods.

IV. Telescopic tubes for the insertion of thermocouple fuel elements.

V. Means for the withdrawal or replacement of a distance tube.

In FIGURES 3 and 4, the lines I-VII, IIVII etc. are taken through the centre of each servicing mechanism. FIGURE 4 is a composite section taken generally a little above the main lift drums in a manner which will be described in more detail with reference to each mechanism in turn.

Turning first to the means for withdrawal or replacement of the control rods and their equipment, details of the servicing mechanism are illustrated in FIGURES 5 and 6, which may be regarded as sections along the line VI-VII of FIGURES 3 and 4 although in FIGURES 5 and 6 the mechanism is shown in two different extended positions. The mechanism is arranged to be brought into either of these extended positions through a parallel link motion; the two links 25, 26 are connected at one end to the inside wall of the vessel 1 and at the other to opposite ends of a movable storage unit 27. This storage unit 27 comprises a lead shield 28 for the control rod, towards the bottom of which is attached a movable support 29 while at its top is afiixed the metal extension 30 for the various associated pulleys. Movement outwards of the storage unit 27 is effected by gravity, and the extent of such outward movement is governed by cables running from main lifting drums 31 around a pulley 32 on the metal extension 3t These main lifting drums 31 are driven through pinions or gears (not shown) from one of the drive units 13; this may be seen more clearly in FIGURE 4, where the lifting drums 31 are depicted without their lines for the sake of clarity and the view is taken from immediately above these drums looking downwards through the vessel 1.

The movable storage unit 27 is shown in FIGURE 5 in its first extended position. In this position, a grab 33 at the end of two steel lifting cables 34 lies on the central axis of the auxiliary vessel 1. The steel lifting cables 34 pass over a pulley 35 on the metal extension 30 to two drums 36. Two further drums 37 disposed outwardly of the drums 36 at the same horizontal level (see FIGURE 3) are used to control further lifting cables 38 passing down to a pulley-type grab 39 at the top of the control rod shield 28. The four drums 36, 37 are driven from two further drive units 13. The drive units disposed above one another on either side of the mechanism are connected by plates 49 between which the drums 31, 36 and 37 are disposed. Further electric lines 41 which are necessary for operation of the grabs 33 and 39, are taken round the top of the mechanism and down to pulley and block take-up means 42 which obviate the need for further winding drums.

In order to appreciate the way in which the mechanism shown in FIGURES 5 and 6 is carried into operation, it is first necessary to refer to FIGURE 7, and in particular to part A thereof which shows the control rod and its associated equipment in its normal position in the reactor. Referring now to FIGURE 7, which shows a series of three vertical sections through the reactor from the top of the standpipes 3 down into the reactor core, each standpipe 3 passes first through the biological shield 2 and subsequently through the outer enclosing shell 43 of the reactor and an inner heat resistant shell 44 which, together with a boron shield 45, is arranged to reduce the temperature of the main enclosing shell 43 above the reactor core. The standpipes 3 pass through the inner heat resistant shell 44 but are welded or otherwise secured to the enclosing shell 43 and the boron shield 45.

The reactor core itself, which is indicated only schematically at 46 in FIGURE 7, consists of many units of graphite moderating material and is provided with over 3,000 vertical fuel element channels such as 47, each of which accommodates 10 fuel elements. Carbon dioxide under pressure is arranged to flow upwards through the vertical channels 47 so as to act as a cooling medium abstracting heat from the fuel elements during operation of the reactor and subsequently passing to heat exchangers, where the heat given up by the gas is used to generate steam for turbo-alternator plant. The enclosing shell 43 must therefore be capable of withstanding pressure of the gas within it, and the auxiliary vessel 1 must also be capable of withstanding full gas pressure and of being sealed in a gas-tight manner to the top of a standpipe 3, since servicing of the reactor will normally be carried out under full operating conditions. In addition to the fuel element channels 47, there are provided a number of smaller diameter vertical channels 48 for control rods such as 49 (FIGURE 7A) of neutron absorbing material. At the top of the reactor core 46 are disposed guide pans 50 with suitable apertures for the channels 47, 48.

Considering now FIGURE 7A in detail, the control rod 49 is shown suspended in its operating position by a cable 51. A distance tube 52 rests on the top of the guide pan 50 and extends up into the standpipe 5; the main function of this distance tube 52 is to prevent the substantial fiow of gas across the top of the reactor core from displacing the control rod 49 and causing its repeated contact with the wall of the channel 48, which might cause damage to the rod. The cable 51 passes through a concrete plug 53, and is arranged to be played out from a conical winch drum 54. The winch drum 54 is driven through bevel gears 55 from a motor 56, The supply leads to which are taken out through the standpipe 3 in a manner not shown in the figure. The top 57 of the standpipe 3 is detachable from the main part of the standpipe through external operation of a gas-tight seal 58 and is provided with a grab head 59. Suspended from the detachable top 57 of the standpipe 3 through chains 60 is a platform 61 which, in the position shown, rests upon three upstanding flanges or ledges 62 integral with the lower part of the standpipe; the motor 56 rests upon it, and the winch drum 54 and concrete plug 53 are suspended from the platform 61 through metal extensions 63. It will be appreciated, therefore, that the control rod 49 and all its associated equipment may be withdrawn as a whole by effecting detachment of the seal 58 and pulling the detachable head 57 of the standpipe upwards by the grab head 59; the motor 56 on the platform 61, winch drum 54, concrete plug 53 and control rod 4? on its cable 51 then being moved vertically upwards. In order that this operation should be performed without disturbance of the cooling medium conditions within the enclosing shell 43 it is first necessary to purge the vessel 1 and fill it with carbon dioxide to an equivalent pressure, so that the interior conditions of the vessel 1 and shell 43 are matched. The vessel 1 is sealed to the flange 12 through a spacer sleeve 11 as shown in FIGURE 2, so that detachment of the seal 58 may be effected without disturbance of the cooling medium conditions and communication between the vessel 1 and the interior of the shell 43 made through the passage defined by the standpipe 3.

Returning now to FIGURES 5 and 6 and considering these in conjunction with FIGURE 7A, it will be seen that FIGURE 5 represents the condition where the control rod and its associated equipment has just been raised vertically upwards until the detachable head 57 of the standpipe is in its final storage position with reference to the metal extension 30 of the movable storage unit 27. This has been effected by movement of the storage unit 27 into its first operative position followed by lowering of the grab 33 until its electrically operated teeth engage upon the grab head 59, followed by winding up of the lifting cables 34 upon the drums 36. Subsequently, a pulley 64, which may be moved towards the central axis of the auxiliary vessel 1 by a piston and cylinder arrangement 65, is arranged to be extended so as to move the control rod cable 51 a little oif the axis and keep the lower part of this cable stationary while the movable storage unit 27 assumes its second operative position shown in FIGURE 6. The pulley-type grab 39 is then lowered and engages the cable 51 in the region of the pulley 64, which is once more retracted. Upon upward movement of the grab 36, the cable 51 is pulled up inside the lead shield 28 which has a slit cut in one side from the bottom to a position corresponding to the lower end of the concrete plug 53. Further movement of the grab 39 then loops the cable 51 until, when the grab 39 has reached the top of the lead shield 28, the control rod 49 is arranged to lie totally within the shield as shown in FIG. 6. To ensure that the control rod 49 also assumes its correct position at the conclusion of the operation, it is necessary that the cable 51 should be fully extended from the winding drum 54 before commencement of the operation. Finally, the movable storage unit 27 is totally retracted once more into its inoperative position, which is that at which the plan view of FIGURE 3 and sectional view of FIGURE 4 are taken.

The above servicing mechanism has been described in detail, because the operation of removing or replacing control rods with their associated equipment is the most fundamental which the reactor servicing operation can be effected, it is essential that the control rod and equipment be first removed so that access may be gained to the core. The operation of replacement of a new control rod and equipment will be obvious in view of the above, and for convenience the auxiliary vessel is provided with two identical servicing mechansms of this sort so that, if necessary, one mechanism may remove the old control rod and equipment and the other may insert a new control rod and equipment in a single sequence of operations. These identical mechanisms are indicated at II and VI in FIGURES 3 and 4, and although FIGURES 5 and 6 have been described as equivalent to the section VI-VII (FIGURE 6 also shows in dotted outline the extension VII-III of this section) it is evident that it may be considered equally well to be a section along II-VII.

Turning now to two further servicing operations, namely the recovery of control rods detached from their cables and the withdrawal of a distance tube, the servicing mechanisms for performing these two operations are substantially identical and it is convenient to refer to them both together. Thus, although FIGURES 8 and 9 refer to distance tube withdrawal and correspond to the section V-VII in FIGURES 3 and 4, they may equally apply to recovery of detached control rods and so be considered equivalent to the section IH-VII. Before referring to FIGURES 8 and 9, it is convenient briefly to describe the sections B and C of FIGURE 7.

It will be evident from FIGURE 7A that, after the control rod 49 has been removed together with its associated equipment, the distance tube 52 will remain in position. It is necessary for other service operations to remove this distance tube, and for this purpose a long arrow-shaped grab 66 (FIGURE 7B) with a telescopic extension 67 is employed. Extendable catches 68 in the grab 66 may be remotely operated to engage recesses (not shown) in the top of the distance tube 52, whereupon this tube may be withdrawn by means of the grab hoisting cable 69. The telescopic extension 67 would normally be brought out to its full length during this operation so that the arrow head engages for locating purposes in the top of the channel 48, but in FIGURE 7B there is also shown a control rod 49 with its cable 51 broken and the telescopic extension 67 is therefore stopped so as not to foul the top of the control rod. In recovering such a broken control rod, the first step would be the removal of the distance tube 52 as shown in FIGURE 75, after which an electrically or gas-operated grab 70 is lowered on the end of two cables 71. The grab 70 slides in a tubular grab guide '72 at the upper end of which there is a flange '73 arranged to rest on the flanges or ledges 62. Operation of the grab 70 so as to grasp hold of the control rod 49 is followed by retraction of the grab, grab guide 72 and control rod 49 back into the vessel 1.

FIGURES 8 and 9 simply show the distance tube withdrawal mechanism in extended and retracted (inoperative) positions respectively, and as previously mentioned they may be considered also illustrative of the recovery of detached control rods since the two mechanisms are identical. Parts which perform the same operations as in FIGURES and 6 have been given the same reference numerals; in this case, however, there are only two lifting drums 36 at the top of the side of the vessel 1 and these operate to withdraw or extend grab cables 69. A supply of carbon dioxide or of electricity for operation of the grab 66, together with an electric line for rnicroswitches, are shown only schematically at 74 and 75 in FIGURE 8, but they run ultimately to the pulley and block take-up means 42. The lead shield 28 in this case has a simple rectangular metal extension 76. The operation of the mechanism will be evident from what has already been described, and it is thought that no further explanation is necessary. FIGURE 8 also shows in dotted lines the mechanism for the removal and replacement of control rods and associated equipment in its retracted position; this corresponds to the section VII-II in FIGURES 3 and 4.

The structure and operation of the two telescopic tube servicing mechanisms I and IV (FIGURES 3 and 4) remain to be described. Referring now to FIGURES 10 and 11, which correspond to the section IV-I in FIG- URES 3 and 4, the figures show two substantially identical sets of telescopic tubes which are, however, separate servicing mechanisms designed to carry out different service operations upon the reactor. The telescopic tubes 77 within their framework 78 constitute means for lowering thermocouple fuel elements into the fuel element channels, while the further telescopic tubes '79 within their corresponding framework 80 are general purpose tubes which may be employed for a variety of operations. Included in these operations is the ramming of a fuel element which may have become lodged in a fuel element channel in the reactor core, the lowering of a television camera into the core and the lowering of a grab right through the reactor core to power means partially or wholly stowed within an auxiliary vessel so as to effect charge or discharge of fuel elements in accordance with the specifications of applications Serial Nos. 686,072, dated September 25, 1957, and 596,114, dated July 5, 1956. This latter operation may be necessary if for any reason a fuel element has become lodged in the lower auxiliary vessel. Each of the telescopic tube mechanisms is shown in its inoperative and extended conditions in FIGURES 10 and 11 and the details of the operation of these mechanisms substantially follow those previously described. In this case, however, the lifting cables 81, 82 for the tubes 77, 79 respectively pass over pulleys at opposite ends of the top links to winding drums 3d situated a short Way down the vessel. In order to illustrate these drums, the sectional plan of the top telescopic tubes in FIGURE 4 is taken just past the lifting drums 31, while the bottom telescopic tubes are shown in a sectional plan taken a little above the cable winding drum 36. The pulley and block take-up means 42 is employed for two carbon dioxide gas supply lines and electrical cables indicated generally at 83. Pressure rollers 84 may be included to keep the main cable 82 in contact near the top pulleys, and either of the telescopic tubes may be assisted in their initial lowering by piston and cylinder arrangements (not shown). Further details of the structure and operation of the thermocouple fuel element telescopic tubes 77 and general purposes telescopic tubes 7% will be described with reference to FIGURES 12 and 13, which show details of operations performed upon the reactor.

FIGURE 12 shows the operation of the general purpose telescopic tubes and includes an introductory section (12A) indicating the removal of a distance tube 52 in the manner already described. After removal of the distance tube, the telescopic tubes 79 are lowered and the operation commences. One of the cables 82, which is stationary, at the stage indicated in FIGURE 12B, carries carbon dioxide gas to a cylinder and piston arrangement 83 which governs the radial upward movement of parallel linkage arms 84 until a housing 85 is located opposite the mouth of whichever fuel element channel 47 is to be serviced. The other cable 87. is movable, being driven round pulleys in the link mechanism and the housing 35 and extending downwards for the operation of whichever apparatus is to be used. FIGURE 12B shows apparatus comprising a pneumatically operated ram 86 having a head 87 in contact with the top of the uppermost fuel element 83. In FIGURE 12C, the ram 86 is shown replaced by a television camera 89 for the inspection of the core 46.

FIGURE 13 shows four successive stages in the insertion of a thermocouple fuel element by means of the other telescopic tube mechanism. The distance tube 52 is assumed already to have been removed, and FIGURE 13A shows the telescopic tubes 77 immediately prior to their location by means of an integral spigot in a control rod hole in guide paragraph 50. The thermocouple leads 90 extend from the thermocouple fuel element 91 carried at the base of the telescopic tubes up to a thermocouple lead drum 92 held upon an outer sleeve 93 fixed to one of the telescopic tubes 77.

It would be inconvenient to arrange for separate motor operation of the drum 92, and in addition the thermocouple leads 90 are encased in heat resistant pyrotenax tubing which is not easily Wound, so that the thermocouple fuel element 91 has its leads 9t almost totally extended even while within the vessel 1. Thus, referring again to FIGURES l0 and 11, the thermocouple lead drum 92 would be in a position approximately as shown, while the thermocouple fuel element 91 will be located at the base of the telescopic tubes 77 within their framework 78. Only a short length of the thermocouple leads 90 is therefore wound upon the drum 92 at any time. It will be seen that in FIGURE 13A there is provided a receiving bracket 94 integral with the standpipe 3, and in FIGURE 138 the further movement of the lower of the two telescopic tubes 77 with respect to the sleeve 93 has operated a cam (not shown) effecting detachment of the drum 92, which is now fixed on the receiving bracket 94.

Also shown in FIGURE 13B is a double piston and cylinder arrangement contained in the lower part of the telescopic tubes 77 The two cylinders 95 of this arrangement are in a fixed position relative to each other and their pistons, such as 96, are arranged to act in opposite directions. At the end of each of the two pistons 96 is a pulley 97, and a wire rope 98 is arranged to be connected at its two ends to fixed parts of the arrangement while passing over both the pulleys 97. This is done in such a way that a trolley 99 firmly attached to the wire rope 98 traverses almost the whole length of the arrangement when the cylinders 95 and pistons 96 are operated to change the positions of the pulleys 97. Comparison of FIGURES 13C and 1313 will show the two positions of the trolley 9 connected to the arrangement. The trolley 99 is also rigidly attached to that one of the cables 81 which passes down to the thermocouple fuel element 91,

- so that the movement of the trolley effects the lowering of this element M into position as shown in FIGURE 13C. Finally, the trolley 99 is releasably attached to the thermocouple leads 90 so that its downward movement also brings the remaining length of these leads off the drum 92. After lowering, the thermocouple fuel element 91 is released from its grab 100. The whole telescopic tubes mechanism is then folded back into line with the standpipe 3 and removed into the vessel 1. On subsequent replacement of the control rod 49 and its associated equipment, the situation is as shown in FIGURE 13D. A further function of the general purpose telescopic tubes 79 is to lower shears down through the standpipe 3 so as to cut the thermocouple leads 90 when it is desired to discharge the thermocouple fuel element 91 through the base of the reactor core 46.

I claim:

1. In a pressurized gas-cooled nuclear reactor of the kind including a reactor core housed within an enclosing shell, said shell providing a plurality of spaced normally closed points of access to said core, an apparatus for performing a multiplicity of distinct different servicing operations for said reactor, said apparatus comprising a travelling auxiliary pressure vessel constructed to withstand the full gas pressure of the reactor, an opening in said auxiliary pressure vessel, gas-tight sealing means for said opening, said sealing means being constructed to provide a gas-tight seal between said auxiliary pressure vessel and any selected one of said points of access, a plurality of distinct different separate selectively operable core servicing mechanisms for servicing a reactor core in said shell, said servicing mechanisms being disposed within said auxiliary pressure vessel, and positioning means for each said servicing mechanism, each said positioning means being disposed at least in part within said auxiliary vessel and constructed to bring its said mechanism selectively into operational position relative to said opening, whereby to place its said mechanism in readiness to be passed into the enclosing shell through a selected point of access as and for the purpose aforesaid.

2. In a pressurised gas-cooled nuclear reactor of the kind including a reactor core housed within an enclosing shell, said apparatus performing a multiplicity of distinct different servicing operations for said reactor, said apparatus comprising a plurality of stand pipes on said shell, said stand pipes being constructed to provide a number of spaced normally closed points of access to said shell, a travelling auxiliary pressure vessel constructed to withstand the full gas pressure of the reactor, an opening in said auxiliary vessel which vessel is otherwise closed, gas-tight sealing means for said opening, said sealing means being constructed to provide a gas-tight seal between said auxiliary vessel and any selected one of said stand pipes and to provide mutual access between said vessel and said shell at said selected stand pipe with the reactor under full operating conditions, and said auxiliary vessel including a plurality of distinct different separate selectively operable core servicing mechanisms for servicing a reactor core in said shell, said servicing mechanisms being disposed within said auxiliary vessel about said opening therein, means mounting each said mechanism for extension through said opening and through said selected standpipe into the enclosing shell for the performance of a particular servicing operation on the core, and positioning means for each said servicing mechanism, each said positioning means being disposed at least in part within said auxiliary vessel and being constructed to bring its said mechanism selectively into operational position relative to said opening, whereby to place its said mechanism in readiness to be passed into the enclosing shell through a selected standpipe as and for the purpose aforesaid.

3. Apparatus as set forth in claim 2, wherein the aux iliary vessel is substantially cylindrical, wherein the opening in the auxiliary vessel with which the core servicing mechanisms are selectively adapted to be brought into operational alignment is substantially centrally located in the base of said auxiliary vessel, and wherein the core servicing mechanisms disposed within the auxiliary vessel are located at spaced intervals on and around the inner wall of said vessel.

4. Apparatus as set forth in claim 3, wherein the positioning means comprise parallel-linkages.

5. Servicing apparatus for performing a multiplicity of distinct different servicing operations upon the core of a gas cooled nuclear reactor of the kind in which the reactor core is housed within enclosing shell having a plurality of spaced points of access to said core, said apparatus comprising a transportable auxiliary vessel, said vessel having a servicing opening, gas-tight sealing means for said opening to provide a gas-tight seal between said opening and any selected one of said points of access, means for transporting said vessel to each of a plurality of spaced servicing positions, a plurality of separate selectively operable distinct different servicing mechanisms for performing said servicing operations, said mechanisms being disposed within said vessel about said servicing opening, positioning means for each said servicing mechanism for bringing its said servicing mechanism selectively into operational position relatively to said opening, and means for extending the selected servicing mechanism through said opening into an operative position.

6. In a pressurized gas cooled nuclear reactor having a reactor core housed within an enclosing shell, said shell having a plurality of spaced points of access, servicing apparatus for performing a multiplicity of distinct different servicing operations on said core comprising a transportable auxiliary pressure vessel, said vessel having an opening therein, means for transporting said vessel into a registering position with any selected one of said points of access, sealing means for providing a gas-tight coupling between said opening and the selected said point of access, to provide mutual access between said auxiliary vessel and said shell at any selected point of access with the reactor under full operating conditions, a plurality of separate selectively operable distinct different servicing mechanisms for performing said servicing operations, said mechanisms being disposed within said vessel about said opening therein, positioning means for pcsitioning each said service mechanism for bringing its said servicing mechanism selectively into an operational position relatively to said opening, and means for extending the selected servicing mechanism through said opening and selected point of access into an operative position with respect to the reactor core.

7. In a pressurized gas cooled nuclear reactor having a reactor core housed within an enclosing shell, means for performing a multiplicity of distinct different servicing operations upon said core comprising a number of standpipes on said shell, said standpipes providing a plurality of spaced points of access to said core, detachable closure means for said standpipes, a transportable auxiliary pressure vessel having a servicing opening therein, means for transporting said auxiliary vessel into a registering position with any selected one of said standpipes, sealing means for providing a gasatight coupling between said opening and any selected standpipe, means for detaching said detachable closing means, a plurality of separate selectively operable distinct dilferent servicing mechanisms for performing said servicing operations, said mechanisms being disposed within said vessel about said servicing opening, positioning means for each said servicing mechanism for bringing its said servicing mechanism selectively into an operational position relatively to said opening, and means for extending the selected servicing mechanism through said opening and standpipe into an operative position with respect to the reactor core.

8. In a pressurized gas cooled nuclear reactor having a reactor core formed with vertical channels, said core being housed within an enclosing shell, means for performing a multiplicity of distinct different sen/icing operations upon said core comprising a number of vertical standpipes on said shell, said standpip'es providing a plurality of spaced points of access to said core, detachable closure means for said standpipes, a transportable auxiliary vessel mounted upon said enclosing shell, means for transporting said auxiliary vessel horizontally into a registering position with any selected one of said standpipes, sealing means for coupling said opening to a selected standpipe, means for detaching said detchable closure means, a plurality of separate selectively operable distinct different servicing mechanism for performing said servicing operations, said mechanisms being disposed within said vessel about said servicing opening, parallel linkage mechanism coupled to each said servicing mechanism for bringing the servicing mechanism selectively into an operational position relatively to said opening, and hoist means for extending the selected servicing mechanism 12 2,936,273 5/60 Unltermyer 60-108 3,025,226 3/62 Martin 61; a1 17632 OTHER REFERENCES l P p g and StEmdPiPe into an Operative P 5 Nucleonics, May 1956, page 110; January 1955, pages sition with respect to the reactor core. 52 55 McLain et 211.: Problems in Nuclear En ineering, vol. References and by the Exammer I, pp. 267, 271-272. A paper presented a? the First Nu- UNITED STATES PATENTS clear Engineering and Science Congress, Cleveland, Ohio, 1,804,843 5/31 Santiago 254 30 X 12-161 1955- 2,725,993 12/55 Smith 214-23 2,848,404 8/58 Treshow 176 44 CARL D. QUARFORTH, P/zmary Examiner. 2,863,815 12/58 Moore et a1. 17629 REUBEN EPSTEIN, Examiner. 

1. IN A PRESSURIZED GAS-COOLED NUCLEAR REACTOR OF THE KIND INCLUDING A REACTOR CORE HOUSED WITHIN AN ENCLOSING SHELL, SAID SHELL PROVIDING A PLURALITY OF SPACED NORMALLY CLOSED POINTS OF ACCESS TO SAID CORE, AN APPARATUS FOR PERFORMING A MULTIPLICITY OF DISTINCT DIFFERENT SERVICING OERATIONS FOR SAID REACTOR, SAID APPARATUS COMPRISING A TRAVELING AUXILIARY PRESSURE VESSEL CONSTRUCTED TO WITHSTAND THE FULL GAS PRESSURE OF THE REACTOR, AN OPENING IN SAID AUXILIARY PRESSURE VESSEL, GAS-TIGHT SEALING MEANS FOR SAID OPENING, SAID SEALING MEANS BEING CONSTRUCTED TO PROVIDE A GAS-TIGHT SEAL BETWEEN SAID AUXILIARY PRESSURE VESSEL AND ANY SELECTED ONE OF SAID POINTS OF ACCESS, A PLURALITY OF DISTINCT DIFFERENT SEPARATE SELECTIVELY OPERABLE CORE SERVICING MECHANISMS FOR SERVICING A REACTOR CORE IN SAID SHELL, SAID SERVICING MECHANISMS BEING DISPOSED WITHIN SAID AUXILIARY PRESSURE VESSEL, AND POSITIONING MEANS FOR EACH SAID SERVICING MECHANISM, EACH SAID POSITIONING MEANS BEING DISPOSED AT LEAST IN PART WITHIN SAID AUXILIARY VESSEL AND CONSTRUCTED TO BRING ITS SAID MECHANISM SELECTIVELY INTO OPERATIONAL POSITION RELATIVE TO SAID OPENING, WHEREBY TO PLACE ITS SAID MECHANISM IN READINESS TO BE PASSED INTO THE ENCLOSING SHELL THROUGH A SELECTED POINT OF ACCESS AS AND FOR THE PURPOSE AFORESAID. 